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23 Jul 2001

Volume 79, Issue 4, pp. 449-553

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Optical spectroscopy on individual CdSe/ZnMnSe quantum dots

G. Bacher, H. Schömig, M. K. Welsch, S. Zaitsev, V. D. Kulakovskii, A. Forchel, S. Lee, M. Dobrowolska, J. K. Furdyna, B. König, and W. Ossau

Appl. Phys. Lett. 79, 524 (2001); http://dx.doi.org/10.1063/1.1387256 (3 pages) | Cited 32 times

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Optical single dot studies in wide-band gap diluted magnetic CdSe/ZnMnSe quantum dots have been performed. Due to the sample design, the photoluminescence energy of the quantum dot signal is energetically below the internal Mn2+ transition, resulting in high quantum efficiencies comparable to nonmagnetic CdSe/ZnSe quantum dots. Magnetic-field- and temperature-dependent measurements on individual dots clearly demonstrate the exchange interaction between single excitons and individual Mn2+ ions, resulting in a giant Zeeman effect and a formation of quasi-zero-dimensional magnetic polarons. © 2001 American Institute of Physics.
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78.67.Hc Quantum dots
73.21.La Quantum dots
78.55.Et II-VI semiconductors
75.50.Pp Magnetic semiconductors
75.75.-c Magnetic properties of nanostructures
71.35.Ji Excitons in magnetic fields; magnetoexcitons
71.70.Gm Exchange interactions
78.20.Ls Magneto-optical effects
71.38.-k Polarons and electron-phonon interactions

Molecular spectroscopy of dye aggregates by scanning-tunneling-microscope-induced light emission

F. Touhari, E. J. A. J. Stoffels, J. W. Gerritsen, H. van Kempen, and P. Callant

Appl. Phys. Lett. 79, 527 (2001); http://dx.doi.org/10.1063/1.1383570 (3 pages) | Cited 14 times

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A bromide-modified silver (111) surface, covered by Jelly-type aggregates of a cyanine dye, is investigated by scanning tunneling microscopy (STM) in air. We show that, under appropriate conditions, light is emitted out of the junction by inelastic electron tunneling. Study of the relation between the light intensity and the tunnel bias clearly reveals a molecular influence on the light emission. Furthermore, through a spectral analysis, we show that sharp resonances appear for dye-covered surfaces by coupling of tip-induced plasmons with molecular excitations. This demonstrates that through STM-induced luminescence local spectroscopic information can be obtained on molecules. © 2001 American Institute of Physics.
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78.60.-b Other luminescence and radiative recombination
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Nanoscale control of ferroelectric polarization and domain size in epitaxial Pb(Zr0.2Ti0.8)O3 thin films

P. Paruch, T. Tybell, and J.-M. Triscone

Appl. Phys. Lett. 79, 530 (2001); http://dx.doi.org/10.1063/1.1388024 (3 pages) | Cited 88 times

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We demonstrate that atomic force microscopy can be used to precisely manipulate individual sub-50 nm ferroelectric domains in ultrahigh density arrays on high-quality epitaxial Pb(Zr0.2Ti0.8)O3 thin films. Control of domain size was achieved by varying the strength and duration of the voltage pulses used to polarize the material. Domain size was found to depend logarithmically upon the writing time and linearly upon the writing voltage. All domains, including those written with ∼100 ns pulses, remained completely stable for the 7 day duration of the experiment. © 2001 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.37.Ps Atomic force microscopy (AFM)
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization

Characteristics of two Coulomb blockade transistors separated by an island to which an oscillating potential is applied: Theory and experiment

Thomas Altebaeumer, Shuhei Amakawa, and Haroon Ahmed

Appl. Phys. Lett. 79, 533 (2001); http://dx.doi.org/10.1063/1.1386615 (3 pages) | Cited 3 times

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Two Coulomb blockade devices connected in series and separated by a main island to which a rf signal was applied, are characterized electrically. The main island is large enough so that Coulomb phenomena in it can be neglected. Although no source–drain voltage is applied, the rf signal causes a current. The polarity of this current depends on the dc gate voltages, which control the two Coulomb blockade devices. The experimental data correspond closely to the simulations. Furthermore, it is evident from theoretical considerations that the circuit can pump electron packets against an applied potential. © 2001 American Institute of Physics.
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85.35.Ds Quantum interference devices
85.35.Gv Single electron devices
73.23.Hk Coulomb blockade; single-electron tunneling

Parallel integration and characterization of nanoscaled epitaxial lattices by concurrent molecular layer epitaxy and diffractometry

T. Ohnishi, D. Komiyama, T. Koida, S. Ohashi, C. Stauter, H. Koinuma, A. Ohtomo, M. Lippmaa, N. Nakagawa, M. Kawasaki, T. Kikuchi, and K. Omote

Appl. Phys. Lett. 79, 536 (2001); http://dx.doi.org/10.1063/1.1385587 (3 pages) | Cited 30 times

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A material highway for building up crystal lattices and heterojunctions from molecular layers has been developed based on a concept of combinatorial lattice integration. The atomic-scale precision of automated multilane paving of multilayered thin films is in situ monitored by concurrent reflection high-energy electron diffraction. The designed nanolayered structures are rapidly verified by a concurrent x-ray diffractometer which has been developed for the purpose of this technology. This scheme corresponds to the concurrent two-dimensional Merrifield synthesis to form a variety of sequence-controlled layer structures in parallel and should be widely applicable for systematic fabrication and property screening of nanostructured materials and devices. © 2001 American Institute of Physics.
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81.16.Rf Micro- and nanoscale pattern formation
81.07.Lk Nanocontacts
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.Cd Superlattices
61.46.-w Structure of nanoscale materials

Sharp photoluminescence of CdS nanocrystals in Al2O3 matrices formed by sequential ion implantation

M. Ando, Y. Kanemitsu, T. Kushida, K. Matsuda, T. Saiki, and C. W. White

Appl. Phys. Lett. 79, 539 (2001); http://dx.doi.org/10.1063/1.1387259 (3 pages) | Cited 16 times

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We report on photoluminescence (PL) experiments in CdS nanocrystals fabricated by sequential ion implantation in Al2O3 matrices. The PL spectrum and the spatial image of the PL intensity have been studied at 8 K using a scanning near-field optical microscope. The PL spectrum at each bright spot has been found to consist of narrow lines of various energies, although the spectrum measured by conventional optics shows a single and broad band locating below the free-exciton absorption energy. The origin of the sharp PL lines in CdS nanocrystals will be discussed. © 2001 American Institute of Physics.
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78.55.Et II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
61.72.up Other materials

Nanostructural study of the thermal transformation of diamond-like amorphous carbon into an ultrahard carbon nanocomposite

L. J. Martínez-Miranda, M. P. Siegal, and P. P. Provencio

Appl. Phys. Lett. 79, 542 (2001); http://dx.doi.org/10.1063/1.1384897 (3 pages) | Cited 6 times

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We studied the structural transformation of diamond-like amorphous carbon (a-C) films into ultrahard carbon nanocomposites via postannealing to 600 °C using transmission electron microscopy, x-ray reflectivity, and small-angle scattering. Film density decreases monotonically above 200 °C. Film surfaces roughen upon annealing to 300 °C; however, a-C recovers its smoothness with higher temperature annealing. Finally, there exists some quasiperiodic nanostructural feature with a lattice spacing that increases with annealing, correlating well with purely a-C nanocomposite structures imaged from samples annealed at 600 °C. We propose that these annealing-induced nanostructural changes are a derivative of localized stress fields in as-grown a-C films. © 2001 American Institute of Physics.
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64.70.Nd Structural transitions in nanoscale materials
68.55.-a Thin film structure and morphology
61.43.Dq Amorphous semiconductors, metals, and alloys
61.46.-w Structure of nanoscale materials
81.05.U- Carbon/carbon-based materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
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Cantilever effects on the measurement of electrostatic potentials by scanning Kelvin probe microscopy

G. Koley, M. G. Spencer, and H. R. Bhangale

Appl. Phys. Lett. 79, 545 (2001); http://dx.doi.org/10.1063/1.1384004 (3 pages) | Cited 45 times

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Scanning Kelvin probe microscopy (SKPM) is a unique way to measure electrostatic potentials for small geometries. It has numerous applications including characterization of integrated circuits and nanoscale devices. SKPM is attractive because of the quantitative nature of the measurements. In this work, we have examined one of the principal sources of measurement error, the cantilever (which holds the probe tip). The accuracy of measurements of electrostatic potentials on closely spaced regions biased differently is reduced due to a large capacitance gradient associated with the cantilever. However, it is observed that the accuracy of measurements increases as the tip–sample distance is decreased because the capacitance gradient of the tip becomes proportionally larger relative to that of the cantilever. It is further observed that longer tips with smaller cantilever areas measure the electrostatic potentials more accurately as the capacitance gradient of the cantilever is reduced. Scanning probe tips are parametrized by a factor R, which indicates their suitability for SKPM measurements. © 2001 American Institute of Physics.
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07.79.-v Scanning probe microscopes and components
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
06.20.Dk Measurement and error theory
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
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High-frequency ultrasound array element using thermoelastic expansion in an elastomeric film

T. Buma, M. Spisar, and M. O’Donnell

Appl. Phys. Lett. 79, 548 (2001); http://dx.doi.org/10.1063/1.1388027 (3 pages) | Cited 19 times

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The thermoelastic effect was used to produce high-frequency, broadband ultrasound in water. A pulsed diode laser, followed by an erbium-doped fiber amplifier, was focused onto a light-absorbing film deposited on a glass substrate. Conversion efficiency was improved by over 20 dB using an elastomeric film instead of a more commonly used metallic one. Radiation pattern measurements show that considerable energy is radiated at +/−45° for frequencies beyond 50 MHz. These results show that the thermoelastic effect can be used to produce phased arrays for high-frequency ultrasound imaging. © 2001 American Institute of Physics.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
83.80.Va Elastomeric polymers
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Quantitative surface stress measurements using a microcantilever

Michel Godin, Vincent Tabard-Cossa, Peter Grütter, and Peter Williams

Appl. Phys. Lett. 79, 551 (2001); http://dx.doi.org/10.1063/1.1387262 (3 pages) | Cited 36 times

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A method for calculating the surface stress associated with the deflection of a micromechanical cantilever is presented. This method overcomes some of the limitations associated with Stoney’s formula by circumventing the need to know the cantilever’s Young’s modulus, which can have a high level of uncertainty, especially for silicon nitride cantilevers. The surface stress is calculated using readily measurable cantilever properties, such as its geometry, spring constant, and deflection. The method is applicable to both rectangular and triangular cantilevers. A calibration of the deflection measurement is also presented. The surface stress measurement is accurate to within 4%–7%. © 2001 American Institute of Physics.
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07.10.Cm Micromechanical devices and systems
07.79.Lh Atomic force microscopes
46.80.+j Measurement methods and techniques in continuum mechanics of solids
07.10.Pz Instruments for strain, force, and torque
06.20.F- Units and standards
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
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