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10 Aug 2009

Volume 95, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 95, 062501 (2009); http://dx.doi.org/10.1063/1.3200226 (3 pages)

O. Vávra, W. Pfaff, and Ch. Strunk
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Speed determination of single Sr adatoms moving within Si(111)-7×7 half unit cells

R. Zhachuk, S. Teys, B. Olshanetsky, and S. Pereira

Appl. Phys. Lett. 95, 061901 (2009); http://dx.doi.org/10.1063/1.3198205 (3 pages) | Cited 2 times

Online Publication Date: 10 August 2009

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In this paper we report on the motion of individual Sr adatoms within the limits of Si(111)-7×7 half unit cells (HUCs). The fast movement of the atom at the Si surface produces sharp signal fluctuations in scanning tunneling microscopy (STM) images resulting into noiselike patches. It is found that the length of the observed image streaks is a function of the scanning tip velocity. A Monte Carlo simulation implementing a model of independently moving Sr adatom and scanning tip, accounts for the observed STM image features quantitatively. Thus, by colleting STM images at various scanning speeds and matching simulated image features to the experimental observations, allows the average speed of Sr adatom within the limits of Si(111)-7×7 HUC to be estimated: 300 nm/s.
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68.35.Fx Diffusion; interface formation
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Quasi-single-crystal (001) SrTiO3 templates on Si

J. W. Park, S. H. Baek, C. W. Bark, M. D. Biegalski, and C. B. Eom

Appl. Phys. Lett. 95, 061902 (2009); http://dx.doi.org/10.1063/1.3202398 (3 pages) | Cited 5 times

Online Publication Date: 10 August 2009

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The integration of multifunctional oxides on semiconductor devices requires the formation of single-crystal-like oxide templates directly on silicon. We report the fabrication of quasi-single-crystal (001) SrTiO3 templates on (001) Si by annealing 100 nm thick molecular beam epitaxy-grown epitaxial SrTiO3 films at 900 °C. The full width at half maximum of the (002) rocking curve is 0.006°, which is much narrower than SrTiO3 bulk single crystals. An atomically smooth TiO2-terminated surface is obtained by buffered-HF etching, which allows us to create functional oxide heterointerfaces on Si. Epitaxial SrRuO3 thin films grown on the quasi-single-crystal SrTiO3 template exhibit a superior crystalline quality and surface morphology.
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68.55.J- Morphology of films
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Cf Surface cleaning, etching, patterning
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Thermoelastic damping in micromechanical resonators

Thomas H. Metcalf, Bradford B. Pate, Douglas M. Photiadis, and Brian H. Houston

Appl. Phys. Lett. 95, 061903 (2009); http://dx.doi.org/10.1063/1.3190509 (3 pages) | Cited 4 times

Online Publication Date: 10 August 2009

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We show that the dominant energy loss mechanism in plate modes of a 1.5 μm thick silicon micromechanical resonator is thermoelastic damping. In situ ultra-high vacuum annealing lowers the dissipation of two neighboring resonance modes (460 and 510 kHz) at 120 K to Q−1 ≤ 5×10−7. From 120 to 400 K, the Q−1 of these modes increase at different rates, in quantitative agreement with a modification (that accounts for mode shape) of Zener’s theory of thermoelastic damping.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
61.72.Cc Kinetics of defect formation and annealing
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

A multiscale approach to diffraction tomography of complex three-dimensional objects

F. Simonetti, L. Huang, and N. Duric

Appl. Phys. Lett. 95, 061904 (2009); http://dx.doi.org/10.1063/1.3204021 (3 pages) | Cited 3 times

Online Publication Date: 11 August 2009

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Tomography of complex three-dimensional objects with diffractive waves remains an open challenge due to the large number of scattering measurements required to obtain a stable solution to the inverse problem of reconstructing an image of the object from a set of independent scattering experiments. Here, this problem is addressed with a multiscale approach that is demonstrated experimentally using ultrasonic waves and which leads to high resolution images comparable to x-ray computerized tomography but without the limitations associated with ionizing radiation.
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42.30.Wb Image reconstruction; tomography
42.25.Fx Diffraction and scattering
87.63.L- Visual imaging

Polarization and temperature dependence of photoluminescence of m-plane GaN grown on γ-LiAlO2 (100) substrate

B. Liu, J. Y. Kong, R. Zhang, Z. L. Xie, D. Y. Fu, X. Q. Xiu, P. Chen, H. Lu, P. Han, Y. D. Zheng, and S. M. Zhou

Appl. Phys. Lett. 95, 061905 (2009); http://dx.doi.org/10.1063/1.3204453 (3 pages) | Cited 1 time

Online Publication Date: 11 August 2009

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We investigated the polarization and temperature dependence of photoluminescence (PL) of m-plane GaN grown on γ-LiAlO2 (100) substrate. The calculated electronic band structure with k•p Hamiltonian points out the energy splitting as well as polarization selection originate from the m-plane GaN epilayer under anisotropic strain. The polarization-angle dependence PL spectra are found to be selected from in-plane x- and z-polarized emission, corresponding to T1 and T2 transition. And the intensity distribution of the fitting peaks satisfies the Malus’ law. An S-shape energy evolution of near band edge peak on temperatures is observed, which originates from the transition between the localized holes and electrons in triangular potentials induced by basal stacking faults.
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78.55.Cr III-V semiconductors
71.20.Nr Semiconductor compounds
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Probing the structural, crystalline, and electrical properties of carbon nanotubes grown on nickel filled carbon nanofibers

Hongxin Zhang, Peter X. Feng, Peng Jin, Vladimir I. Makarov, Luis Fonseca, Gerardo Morell, and Brad R. Weiner

Appl. Phys. Lett. 95, 061906 (2009); http://dx.doi.org/10.1063/1.3204475 (3 pages) | Cited 2 times

Online Publication Date: 11 August 2009

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Carbon nanotubes (CNTs) were produced on nickel filled carbon nanofiber substrates. The carbon source was provided by irradiation of pyrolytic graphite. The mean outer diameter of the CNTs, which was identified as multiwalled carbon nanotubes, varies in the range of 5–15 nm. The crystallographic structures, chemical compositions, and bond structures of the carbon materials were investigated. The modified crystal structure was attributed to better lattice arrangement resulting from increased lattice vibration at high substrate temperature. The improved electron field emission behavior of the obtained sample at higher temperature could be caused by the increasing effective emission sites.
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61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
81.07.De Nanotubes
79.70.+q Field emission, ionization, evaporation, and desorption

Influence of deviatoric stress on the pressure-induced structural phase transition of ZnO studied by optical second harmonic generation measurements

L. Bayarjargal, B. Winkler, E. Haussühl, and R. Boehler

Appl. Phys. Lett. 95, 061907 (2009); http://dx.doi.org/10.1063/1.3205120 (3 pages) | Cited 5 times

Online Publication Date: 12 August 2009

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The pressure-induced B4⇆B1 structural phase transition of ZnO has been studied with the second harmonic generation (SHG) technique. Measurements in nonhydrostatic and hydrostatic pressure transmitting media show slightly different transition pressures (9–11 GPa) and a different pressure dependence of the SHG intensities. These observations are consistent with the presence of a tetragonal and hexagonal intermediate phase as a result of hydrostatic and axial compression, respectively. In contrast to earlier work, it is shown that it is not necessary to use nanocrystalline starting material to be able to recover the B1 phase at ambient conditions.
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62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Characteristics of ultraviolet photoluminescence from high quality tin oxide nanowires

Rui Chen, G. Z. Xing, J. Gao, Z. Zhang, T. Wu, and H. D. Sun

Appl. Phys. Lett. 95, 061908 (2009); http://dx.doi.org/10.1063/1.3205122 (3 pages) | Cited 16 times

Online Publication Date: 12 August 2009

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We investigate the optical properties of ultraviolet range emission from high quality tin oxide nanowires prepared by vapor-liquid-solid growth technique. Temperature dependent photoluminescence (PL) measurement is performed between 10 and 300 K. At low temperatures, the PL originates from radiative recombination of excitons bound to neutral donors, donor-acceptor pair transition and their associated longitudinal optical (LO) phonon replicas. The LO-phonon replicas up to third order with Huang–Rhys factor of 0.34 are observed. Evolution of the peaks and the origin of PL thermal quenching at high temperatures are discussed in detail.
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81.07.Vb Quantum wires
78.67.Lt Quantum wires
78.55.Hx Other solid inorganic materials
78.40.Fy Semiconductors
73.21.Hb Quantum wires
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
71.35.-y Excitons and related phenomena

Optoacoustic response of a single submicronic gold particle revealed by the picosecond ultrasonics technique

Yannick Guillet, Clément Rossignol, Bertrand Audoin, Gaëtan Calbris, and Serge Ravaine

Appl. Phys. Lett. 95, 061909 (2009); http://dx.doi.org/10.1063/1.3205472 (3 pages) | Cited 7 times

Online Publication Date: 13 August 2009

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The optoacoustic response of a single submicron (430 nm) gold particle embedded in a silica thin film is experimentally revealed by femtosecond pump-probe experiments. A semianalytical model is developed to calculate the transient reflectivity accounting for optical index changes in both media and for particle and film surface displacements. The displacement of the particle-film interface turns out to be the major contribution to the measured signal. The amplitude of the acoustical component of the transient reflectivity is modulated by the depth at which the particle is buried in the film.
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78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
62.65.+k Acoustical properties of solids
78.47.J- Ultrafast spectroscopy (<1 psec)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Strong photoluminescence at 1.53 μm from GaSb/AlGaSb multiple quantum wells grown on Si substrate

D. H. Nguyen, J. Park, Y. K. Noh, M. D. Kim, D. Lee, and J. E. Oh

Appl. Phys. Lett. 95, 061910 (2009); http://dx.doi.org/10.1063/1.3205473 (3 pages) | Cited 1 time

Online Publication Date: 13 August 2009

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Strong photoluminescence at 1.53 μm was obtained from a GaSb/Al0.4Ga0.6Sb multiple-quantum-well sample grown on Si substrate, indicating greatly reduced defects by InSb quantum-dot layers that terminate dislocations. The carrier lifetime of 1.4 ns, comparable to typical InP-based quantum wells, and its independence on excitation power indicates the low defect density. Due to the wide well width and tensile strain, photoluminescence was dominated by the light hole-electron transition at low temperature. However, the heavy hole-electron transition was dominant at room temperature due to the proximity of energy levels and higher density of states for the heavy hole transition.
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78.67.De Quantum wells
73.21.Fg Quantum wells
61.72.Lk Linear defects: dislocations, disclinations
73.20.At Surface states, band structure, electron density of states
78.55.Cr III-V semiconductors

Photovoltaic cells fabricated utilizing core-shell CdSe/ZnSe quantum dot/multiwalled carbon nanotube heterostructures

Fushan Li, Dong Ick Son, Tae Whan Kim, Euidock Ryu, Sang Wook Kim, Sun Kyun Lee, and Yong Hoon Cho

Appl. Phys. Lett. 95, 061911 (2009); http://dx.doi.org/10.1063/1.3204696 (3 pages) | Cited 11 times

Online Publication Date: 13 August 2009

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An efficient quenching of the photoluminescence spectrum was observed for the quantum dot (QD)-multiwalled carbon nanotubes (MWCNTs) nanocomposite. While the lifetime of the blue emission from ZnSe shell was significantly reduced, it did not exhibit any obvious change in the red emission from CdSe core-crystal. This difference revealed two competing charge transfer processes between the CdSe core-crystal, the ZnSe shell and the MWCNTs. Current-voltage measurements on devices fabricated utilizing CdSe QD-MWCNT nanocomposites showed photovoltaic (PV) effect under ultraviolet light illumination. Charge transfer mechanisms of the PV cells are described on the basis of the experimental results.
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85.60.-q Optoelectronic devices
85.35.-p Nanoelectronic devices
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