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21 Jan 2002

Volume 80, Issue 3, pp. 341-531

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Optical dispersion, two-photon absorption and self-phase modulation in silicon waveguides at 1.5 μm wavelength

H. K. Tsang, C. S. Wong, T. K. Liang, I. E. Day, S. W. Roberts, A. Harpin, J. Drake, and M. Asghari

Appl. Phys. Lett. 80, 416 (2002); http://dx.doi.org/10.1063/1.1435801 (3 pages) | Cited 99 times

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We measure linear optical dispersion, nonlinear refraction and two-photon absorption in a silicon waveguide at 1.54 μm wavelength. The total dispersion in the silicon waveguide was found to be −9.1 fs/(nm cm). At 1.54 μm wavelength, the two-photon absorption coefficient was found to be 0.45 cm/GW and a π phase shift from self-phase modulation was observed in optical pulses of 60 W peak-coupled power, generated from an amplified gain-switched laser diode. © 2002 American Institute of Physics.
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42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.25.Bs Wave propagation, transmission and absorption
42.25.Gy Edge and boundary effects; reflection and refraction

Mechanisms for hetero-epitaxial nucleation of YBa2Cu3O ∼ 6.1 at the buried precursor/SrTiO3 interface in the postdeposition reaction process

L. Wu, V. F. Solovyov, H. J. Wiesmann, Y. Zhu, and M. Suenaga

Appl. Phys. Lett. 80, 419 (2002); http://dx.doi.org/10.1063/1.1436285 (3 pages) | Cited 18 times

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The mechanisms have been identified for the hetero-epitaxial nucleation of YBa2Cu3O ∼ 6.1 (YBCO) at the buried interface between a precursor film and SrTiO3 for the so-called BaF2 process which is a postdeposition reaction process for the synthesis of epitaxial YBCO films. It is shown that the preferential nucleation of YBCO at the interface is due to (1) the strong chemical affinity of the (Y, Ba)-oxy-fluoride, an intermediate phase, to SrTiO3 and (2) the epitaxial alignment of its (111) planes with the (001) surface of the SrTiO3 which reduces the activation barrier for the formation of YBCO. In thin films (<2–3 μm) the YBCO nuclei, whose c axes are perpendicular to the SrTiO3 surface, form directly from this aligned oxy-fluoride. In thick films (5 μm), however, this oxy-fluoride decomposes into a disordered transitory cubic phase which then orders to form YBCO nuclei with three orientational variants, one with its c axis perpendicular and two with their c axes parallel to the (001) plane of SrTiO3. © 2002 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
68.55.A- Nucleation and growth

Rapid thermal low-pressure metal organic chemical vapor deposition of Fe-doped InP layers

O. Kreinin and G. Bahir

Appl. Phys. Lett. 80, 422 (2002); http://dx.doi.org/10.1063/1.1436278 (3 pages)

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High quality Fe-doped InP layers have been grown by means of rapid thermal low-pressure metal organic chemical vapor deposition. Trimethylindium, tertiarybutylphosphine, and ferrocene were used as indium, phosphorus, and iron sources, respectively. The best growth conditions are: V–III ratio of 100 temperature of 650 °C, pressure of 4 Torr and growth rate of 2 μm/h. Featureless films were grown with a flat iron concentration of 2×1018 cm−3 as a function of depth, with an average specific resistivity of 108 Ω cm and a narrow x-ray half-maximum peak of 15 arcs. © 2002 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Superhard conductive carbon nanocrystallite films

S. Hirono, S. Umemura, M. Tomita, and R. Kaneko

Appl. Phys. Lett. 80, 425 (2002); http://dx.doi.org/10.1063/1.1435402 (3 pages) | Cited 35 times

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Carbon films whose hardness is comparable to diamond’s, but whose electrical conductivity is 19 orders of magnitude larger, have been discovered. The films were deposited onto silicon substrates by electron cyclotron resonance plasma sputtering. The bonding structure of the film was mainly sp2. The film consisted of sp2 nanocrystallites having parallel and curved graphene sheets vertically oriented to the film surface. The sp2 nanocrystallites were connected with adjacent crystallites by sp3 bonding, which gives the film both its high hardness and conductivity. These sp2 nanocrystallite films will have many applications. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.U- Carbon/carbon-based materials
81.07.Bc Nanocrystalline materials
68.60.Bs Mechanical and acoustical properties
52.77.Dq Plasma-based ion implantation and deposition
73.63.Bd Nanocrystalline materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Pq Friction, lubrication, and wear
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Large size dependence of exciton-longitudinal-optical-phonon coupling in nitride-based quantum wells and quantum boxes

S. Kalliakos, X. B. Zhang, T. Taliercio, P. Lefebvre, B. Gil, N. Grandjean, B. Damilano, and J. Massies

Appl. Phys. Lett. 80, 428 (2002); http://dx.doi.org/10.1063/1.1433165 (3 pages) | Cited 34 times

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We present an experimental and theoretical study of the size dependence of the coupling between electron–hole pairs and longitudinal-optical phonons in Ga1−xInxN/GaN-based quantum wells and quantum boxes. We found that the Huang–Rhys factor S, which determines the distribution of luminescence intensities between the phonon replicas and the zero-phonon peak, increases significantly when the vertical size of the boxes or the thickness of quantum well increases. We assign this variation to (1) the strong electric field present along the growth axis of the system, due to spontaneous and piezoelectric polarizations in these wurtzite materials, and (2) the localization on separate sites of electrons and holes in the plane of the wells or boxes, due to potential fluctuations in the ternary alloy. Indeed, envelope-function calculations for free or localized excitons, with electron–hole distance only controlled by Coulomb interaction, do not account quantitatively for the measured behavior of the S factor. In fact, the latter is rather similar to what is obtained for donor–acceptor pairs, with a statistical distribution of distances between localization centers for electrons and holes. © 2002 American Institute of Physics.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
63.20.kk Phonon interactions with other quasiparticles
78.67.De Quantum wells
78.55.Cr III-V semiconductors

Cyclotron resonance and magnetotransport measurements in AlxGa1−xN/GaN heterostructures for x = 0.15–0.30

Z.-F. Li, W. Lu, S. C. Shen, S. Holland, C. M. Hu, D. Heitmann, B. Shen, Y. D. Zheng, T. Someya, and Y. Arakawa

Appl. Phys. Lett. 80, 431 (2002); http://dx.doi.org/10.1063/1.1435074 (3 pages) | Cited 6 times

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Cyclotron resonance (CR) and magnetotransport experiments have been performed on modulation Si-doped AlxGa1−xN/GaN heterostructures with aluminum fraction x varying from 0.15 to 0.30. A clear CR absorption and Shubnikov–de Haas oscillations have been observed. The CR line shapes are analyzed by calculating the high frequency conductivity of a two-dimensional electron gas. The obtained electron effective mass m∗ and scattering time τ are found to depend on the aluminum fraction x. For x = 0.30 the measured CR frequency shifts significantly upward, which demonstrates the formation of potential fluctuations in AlxGa1−xN/GaN heterostructures with large aluminum fraction x. © 2002 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects
76.40.+b Diamagnetic and cyclotron resonances
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.20.At Surface states, band structure, electron density of states

Quantum-interference characteristics of a 25 nm trench-type InGaAs/InAlAs quantum-wire field-effect transistor

T. Sugaya, J. P. Bird, M. Ogura, Y. Sugiyama, D. K. Ferry, and K.-Y. Jang

Appl. Phys. Lett. 80, 434 (2002); http://dx.doi.org/10.1063/1.1434304 (3 pages) | Cited 14 times

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We study the quantum-interference characteristics of a 25 nm, trench-type, InGaAs quantum-wire field-effect transistor realized by selective epitaxy, and find very different behavior from that typically exhibited by disordered wires. The amplitude of the magnetoresistance fluctuations is exponentially suppressed at high fields, where evidence of an Aharonov–Bohm effect is observed. The exponential suppression appears to be consistent with theoretical predictions for the influence of magnetic field on the scattering rate in clean wires, while the Aharonov–Bohm effect points to an interference process in which the one-dimensional subbands of the wire themselves constitute well-resolved paths for electron interference. © 2002 American Institute of Physics.
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85.35.Ds Quantum interference devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.63.Nm Quantum wires
85.30.Tv Field effect devices
72.20.My Galvanomagnetic and other magnetotransport effects
85.30.De Semiconductor-device characterization, design, and modeling

Analysis of photoexcited charge carrier density profiles in Si wafers by using an infrared camera

Rolf Brendel, Michael Bail, Benno Bodmann, Jörg Kentsch, and Max Schulz

Appl. Phys. Lett. 80, 437 (2002); http://dx.doi.org/10.1063/1.1434308 (3 pages) | Cited 2 times

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We demonstrate the mapping of lateral photoexcited charge carrier density profiles in a Si wafer that is illuminated in a spot by strongly absorbed light, using an infrared camera. The radial decay measured for the charge carrier density yields information on the effective carrier lifetime. The lifetime is extracted from the infrared camera image by modeling the transport. The carrier lifetime determined with the infrared camera technique is in accord with results obtained by conventional transient microwave reflectance measurements. © 2002 American Institute of Physics.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors
72.40.+w Photoconduction and photovoltaic effects
81.05.Cy Elemental semiconductors
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Hole and electron field-effect mobilities in nanocrystalline silicon deposited at 150 °C

I-Chun Cheng and Sigurd Wagner

Appl. Phys. Lett. 80, 440 (2002); http://dx.doi.org/10.1063/1.1435798 (3 pages) | Cited 51 times

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Field-effect structures were made from nanocrystalline silicon (nc-Si:H) deposited at a substrate temperature of 150 °C by plasma-enhanced chemical vapor deposition excited at 80 MHz. The nc-Si:H channel layer was grown on top of a separate nc-Si:H buffer and seed layer that serves to develop the crystalline structure. Staggering the contacts and the gate ensures that mobilities are measured precisely in the last-to-grow nc-Si:H layer. The hole mobility in saturation reaches 0.06–0.2 cm2 V−1 s−1 and the electron mobility ∼12 cm2 V−1 s−1. These results suggest that large-area circuits of complementary p- and n-channel devices can be made from nc-Si:H deposited on low-temperature substrates. © 2002 American Institute of Physics.
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73.61.Cw Elemental semiconductors
72.80.Cw Elemental semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.Fr Low-field transport and mobility; piezoresistance
73.63.Bd Nanocrystalline materials

Photoluminescence properties of MgS/CdSe quantum wells and quantum dots

M. Funato, A. Balocchi, C. Bradford, K. A. Prior, and B. C. Cavenett

Appl. Phys. Lett. 80, 443 (2002); http://dx.doi.org/10.1063/1.1435407 (3 pages) | Cited 11 times

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The optical properties of MgS/CdSe quantum structures grown by molecular beam epitaxy are characterized by photoluminescence (PL) spectroscopy. The increase in the CdSe thickness from 1 to beyond 3 ML results in the formation of, at first, quantum wells (QWs) and then quantum dots (QDs) by Stranski–Krastanov growth. The PL temperature dependence measurements reveal that, in the QWs, excitons localized by potential fluctuations principally govern the PL properties, which is in strong contrast to the QD PL properties. © 2002 American Institute of Physics.
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78.55.Et II-VI semiconductors
78.67.De Quantum wells
78.67.Hc Quantum dots
73.21.Fg Quantum wells
71.35.-y Excitons and related phenomena
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.21.La Quantum dots

GaN metal–oxide–semiconductor structures using Ga-oxide dielectrics formed by photoelectrochemical oxidation

D. J. Fu, Y. H. Kwon, T. W. Kang, C. J. Park, K. H. Baek, H. Y. Cho, D. H. Shin, C. H. Lee, and K. S. Chung

Appl. Phys. Lett. 80, 446 (2002); http://dx.doi.org/10.1063/1.1436279 (3 pages) | Cited 30 times

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GaN metal–oxide–semiconductor (MOS) capacitors were fabricated by using Ga oxide formed by photoelectrochemical oxidation of GaN. The electrical properties of the MOS structures as characterized by capacitance–voltage measurement were found to be dependent on the oxidation time and posttreatment. Positive flatband voltage was observed in devices with thin oxide layers indicating the existence of negative oxide charge. Very thin oxide exhibits high capacitance and reverse leakage, which can be reduced by rapid thermal annealing (RTA). Passivation of the interface by RTA is partially responsible for the improvement. Thicker oxide layers exhibit improved electrical properties. Low density of interface states ( ∼ 1011 eV−1 cm−2) was obtained in the Ga-oxide/GaN structure grown under optimized conditions. © 2002 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.65.Mq Oxidation
82.45.-h Electrochemistry and electrophoresis
82.50.-m Photochemistry
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
73.20.At Surface states, band structure, electron density of states
81.05.Ea III-V semiconductors
81.65.Rv Passivation
82.45.Jn Surface structure, reactivity and catalysis
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
84.32.Tt Capacitors
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Properties of a Fe/GaAs(001) hybrid structure grown by molecular-beam epitaxy

Y. Chye, V. Huard, M. E. White, and P. M. Petroff

Appl. Phys. Lett. 80, 449 (2002); http://dx.doi.org/10.1063/1.1434302 (3 pages) | Cited 26 times

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We report on the epitaxy of Fe thin films on GaAs(001) using molecular-beam epitaxy with two different growth methods aimed at suppressing Fe and GaAs interdiffusion. These methods make use of low-temperature deposition at −150 °C and/or of an ultrathin Al interlayer, respectively. Good-quality single-crystal Fe films were obtained. The magnetic properties of the Fe films show square hysteresis loops and clear in-plane magnetic anisotropy with well-defined easy hard axes. The photoluminescence of an Al0.3Ga0.7As/GaAs quantum well in close proximity to the Fe film is measured in order to examine the quality of the Fe/GaAs interface. © 2002 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Ct Interface structure and roughness
68.35.Fx Diffusion; interface formation
68.55.A- Nucleation and growth
68.65.Fg Quantum wells
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.67.De Quantum wells
81.05.Ea III-V semiconductors

Dependences of the activation volumes on Ar sputtering pressure in Co/Pt multilayers prepared by dc magnetron sputtering

Yoon-Chul Cho, Sug-Bong Choe, and Sung-Chul Shin

Appl. Phys. Lett. 80, 452 (2002); http://dx.doi.org/10.1063/1.1435405 (3 pages) | Cited 5 times

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We investigated the wall-motion and nucleation activation volumes of Co/Pt multilayer films prepared by dc magnetron sputtering under various Ar sputtering pressures. Delicate analysis of time-resolved domain evolution patterns reveals that the nucleation activation volume is generally smaller than the wall-motion activation volume in all the samples, which is consistent with the nucleation-dominant magnetization reversal behavior observed in this system. Interestingly, the activation volume is found to decrease with increasing Ar pressure, despite a decreasing trend in saturation magnetization. Decreasing grain size with increasing Ar pressure, smaller than the typical size of a Co single domain, is believed to be the origin of the unexpected observation. © 2002 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
81.15.Cd Deposition by sputtering
68.65.Ac Multilayers
75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms
81.07.-b Nanoscale materials and structures: fabrication and characterization

Interface reaction of Ta/Ni81Fe19 or Ni81Fe19/Ta and its suppression

G. H. Yu, H. C. Zhao, M. H. Li, F. W. Zhu, and W. Y. Lai

Appl. Phys. Lett. 80, 455 (2002); http://dx.doi.org/10.1063/1.1433913 (3 pages) | Cited 10 times

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Ta/Ni81Fe19 and Ni81Fe19/Ta structures are commonly used in the magnetic multilayers with giant magnetoresistance. For a Ta/Ni81Fe19/Ta fundamental structure, Ta seed and Ta cap layers resulted in a loss of moment equivalent to a magnetically dead layer of thickness 1.6±0.2 nm. In order to find out the reason, the composition and chemical states at the interface regions of Ta/Ni81Fe19 and Ni81Fe19/Ta were studied using the x-ray photoelectron spectroscopy and peak decomposition technique. The results show that there are thermodynamically favorable reactions at the Ta/Ni81Fe19 and Ni81Fe19/Ta interfaces: 2Ta+Ni = NiTa2. However, the thickness of a magnetically dead layer was significantly reduced by the insertion of a small amount of Bi in the Ta/Ni81Fe19/Ta structure. This result indicates that a surfactant Bi can suppress the interface reaction in multilayers. © 2002 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
79.60.Jv Interfaces; heterostructures; nanostructures
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Electronic spin detection in molecules using scanning-tunneling- microscopy-assisted electron-spin resonance

C. Durkan and M. E. Welland

Appl. Phys. Lett. 80, 458 (2002); http://dx.doi.org/10.1063/1.1434301 (3 pages) | Cited 96 times

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By combining the spatial resolution of a scanning-tunneling microscope (STM) with the electronic spin sensitivity of electron-spin resonance, we show that it is possible to detect the presence of localized spins on surfaces. The principle is that a STM is operated in a magnetic field, and the resulting component of the tunnel current at the Larmor (precession) frequency is measured. This component is nonzero whenever there is tunneling into or out of a paramagnetic entity. We have succeeded in obtaining spectra from free radical molecules from which the g factor of a spin entity may be inferred. For the molecules studied here, α,γ-bisdiphenylene-β-phenylallyl, g was found to be 2±0.1. © 2002 American Institute of Physics.
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76.30.Rn Free radicals
07.79.Cz Scanning tunneling microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Fabrication of magnetic microfiltration systems using soft lithography

Tao Deng, Mara Prentiss, and George M. Whitesides

Appl. Phys. Lett. 80, 461 (2002); http://dx.doi.org/10.1063/1.1436282 (3 pages) | Cited 54 times

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Arrays of nickel posts were used as magnetic elements in a microfiltration device that is compatible with microfluidic systems. The combination of microtransfer molding—a soft lithography technique—and electrodeposition generated nickel posts ∼7 μm in height and ∼15 μm in diameter inside a microfluidic channel. Once magnetized by a magnetic field from an external, permanent, neodymium–iron–boron magnet, these nickel posts generated strong magnetic field gradients and efficiently trapped superparamagnetic beads moving past them in a flowing stream of water. These nickel post arrays were also used to separate magnetic beads from nonmagnetic beads. © 2002 American Institute of Physics.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
85.70.-w Magnetic devices
85.40.Hp Lithography, masks and pattern transfer
75.50.Ww Permanent magnets
81.15.Pq Electrodeposition, electroplating

Electrical transport and magnetoresistance in thick films of lanthanum calcium manganite prepared by tape casting

G. Srinivasan and E. T. Rasmussen

Appl. Phys. Lett. 80, 464 (2002); http://dx.doi.org/10.1063/1.1436283 (3 pages) | Cited 2 times

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The observation of unique thickness-dependent resistivity and magnetoresistance is reported in thick films of La0.7Ca0.3MnO3 synthesized by tape casting. Samples were prepared from tapes with layer thickness L ranging from 6 to 40 μm. Ferromagnetic resonance was used to probe the homogeneity of the films. The maximum zero-field electrical resistivity ρm(0) and low-field magnetoresistance (MR) data show: (i) an exponential drop in ρm(0) with increasing L (an inverse square dependence) and (ii) an exponential increase in MR with L (a square-root dependence). The results are in qualitative agreement with tunneling-assisted electrical transport. © 2002 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
73.40.Gk Tunneling
75.50.Dd Nonmetallic ferromagnetic materials
75.47.De Giant magnetoresistance
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
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Large remanent polarization and coercive force by 100% 180° domain switching in epitaxial Pb(Zr0.5Ti0.5)O3 capacitor

Junichi Ishida, Takatoshi Yamada, Atsuhito Sawabe, Kumi Okuwada, and Keisuke Saito

Appl. Phys. Lett. 80, 467 (2002); http://dx.doi.org/10.1063/1.1433912 (3 pages) | Cited 14 times

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Pb(Zr0.5Ti0.5)O3 (PZT) thin film was heteroepitaxially grown on an iridium/magnesium oxide (Ir/MgO) (001) substrate using the metalo-organic decomposition method, and its crystal orientation and ferroelectric properties were investigated. The Ir film by rf-magnetron sputtering on a MgO single crystal showed high crystallinity with the full width at half maximum of 0.2°. The obtained PZT film has a tetragonal structure. Reciprocal space mapping revealed that it consisted of only c-axis orientation. The Ir/PZT/Ir capacitor showed the remanent polarization of 45 μ C/cm2 and a coercive force of 100 kV/cm. These large values were derived from 100% 180° domain switching, which state is difficult to realize in bulky single crystal and ceramics because of piezostress relaxation. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
68.55.-a Thin film structure and morphology
77.80.Fm Switching phenomena
85.50.Gk Non-volatile ferroelectric memories

Local electric-field-driven repoling reflected in the ferroelectric polarization of Ce-doped Sr0.61Ba0.39Nb2O6

T. Granzow, U. Dörfler, Th. Woike, M. Wöhlecke, R. Pankrath, M. Imlau, and W. Kleemann

Appl. Phys. Lett. 80, 470 (2002); http://dx.doi.org/10.1063/1.1435403 (3 pages) | Cited 15 times

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We present pyroelectric measurements with the relaxor-ferroelectric strontium barium niobate in the phase transition regime. It is demonstrated that domains poled at high temperatures are more stable than those oriented at room temperature. This yields a higher phase-transition temperature when heating the sample and a strong repoling during the cooling process. We explain this difference within the framework of the random field model for relaxor ferroelectrics. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.70.+a Pyroelectric and electrocaloric effects
77.80.B- Phase transitions and Curie point
77.80.Dj Domain structure; hysteresis
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Lateral redistribution of excitons in CdSe/ZnSe quantum dots

M. Strassburg, M. Dworzak, H. Born, R. Heitz, A. Hoffmann, M. Bartels, K. Lischka, D. Schikora, and J. Christen

Appl. Phys. Lett. 80, 473 (2002); http://dx.doi.org/10.1063/1.1432743 (3 pages) | Cited 36 times

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Lateral redistribution processes of excitons localized in CdSe/ZnSe quantum dot structures are investigated by time-integrated and time-resolved spectroscopy. The photoluminescence properties are governed by lateral energy transfer within a dense ensemble of quantum dots. The quantum dots differ in size and Cd concentration and provide a complex potential landscape with localization sites for excitons. At low temperatures, lateral transfer by tunneling leads to a redshift with increasing delay after pulsed excitation. The mobility edge was determined to 2.561 eV. Above 100 K, thermally activated escape and recapture of excitons cause a strong redshift of the PL maximum in the first 500 ps. © 2002 American Institute of Physics.
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71.35.Cc Intrinsic properties of excitons; optical absorption spectra
73.21.La Quantum dots
78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics

Effects of spatial separation on the growth of vertically aligned carbon nanofibers produced by plasma-enhanced chemical vapor deposition

Vladimir I. Merkulov, Anatoli V. Melechko, Michael A. Guillorn, Douglas H. Lowndes, and Michael L. Simpson

Appl. Phys. Lett. 80, 476 (2002); http://dx.doi.org/10.1063/1.1433905 (3 pages) | Cited 22 times

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Vertically aligned carbon nanofibers (VACNFs) with vastly different spacing were grown by catalytically controlled dc glow discharge chemical vapor deposition. Both densely packed VACNFs and essentially isolated VACNFs were studied using scanning electron microscopy and x-ray energy dispersive spectroscopy. The morphology and chemical composition of isolated VACNFs were found to have a strong dependence upon the growth conditions, in particular on the C2H2/NH3 gas mixture used. This is attributed to the sidewalls of isolated VACNFs being exposed to reactive species during growth. In contrast, the sidewalls of densely packed VACNFs were shielded by the neighboring VACNFs, so that their growth occurred mainly in the vertical direction, by diffusion of carbon through the catalyst nanoparticle and subsequent precipitation at the nanofiber/nanoparticle interface. These striking differences in the growth process result in the formation of flattened carbon nanostructures (carbon nanotriangles) and also are quite important for the realization of VACNF-based devices. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

β-Ga2O3 nanowires synthesized from milled GaN powders

B. C. Kim, K. T. Sun, K. S. Park, K. J. Im, T. Noh, M. Y. Sung, S. Kim, S. Nahm, Y. N. Choi, and S. S. Park

Appl. Phys. Lett. 80, 479 (2002); http://dx.doi.org/10.1063/1.1435073 (3 pages) | Cited 36 times

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White-colored materials synthesized by a thermal annealing of milled GaN powders at 930 °C in a nitrogen atmosphere were identified to be monoclinic β-Ga2O3 nanowires by x-ray diffraction and scanning electron microscopy. High-resolution transmission electron microscopy revealed that these nanowires are single nanocrystals, and energy dispersive x-ray indicated that these nanomaterials are free of any metals. In addition, bundles of these crystalline nanowires in the rectangular-pole shape are a few centimeters in length.© 2002 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.40.Gh Other heat and thermomechanical treatments
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Laser manipulation and fixation of single gold nanoparticles in solution at room temperature

Syoji Ito, Hiroyuki Yoshikawa, and Hiroshi Masuhara

Appl. Phys. Lett. 80, 482 (2002); http://dx.doi.org/10.1063/1.1432753 (3 pages) | Cited 37 times

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A method to fix single gold nanoparticles on glass substrate was demonstrated in solution at room temperature by utilizing focused intense laser beams. A single gold nanoparticle of 80 nm was optically trapped and manipulated to a surface of a glass substrate, and then fixed on it by irradiation with ultraviolet (UV) laser light. Suitable laser fluence range for the fixation was determined to be 32–60 mJ/cm2, above which the individual nanoparticles were fragmented to several smaller fragments of 10 to 40 nm. The fixation mechanism is discussed in view of pulsed-laser-induced transient temperature elevation. © 2002 American Institute of Physics.
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81.16.Ta Atom manipulation
61.46.-w Structure of nanoscale materials
37.10.Vz Mechanical effects of light on atoms, molecules, and ions

InGaN self-assembled quantum dots grown by metalorganic chemical-vapor deposition with indium as the antisurfactant

J. Zhang, M. Hao, P. Li, and S. J. Chua

Appl. Phys. Lett. 80, 485 (2002); http://dx.doi.org/10.1063/1.1433163 (3 pages) | Cited 13 times

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Nanometer-scale InGaN self-assembled quantum dots have been formed in an InGaN single-quantum-well structure on a (0001) sapphire substrate with In as the antisurfactant using low-pressure metalorganic chemical-vapor deposition. High-resolution transmission electron microscopy reveals that the average dimensions of InGaN nanometer-scale structures are as small as 4 nm wide and 1.5 nm high. Strong photoluminescence emission of the InGaN quantum dots was observed at room temperature with an emission peak of about 2.56 eV (485 nm) and a full width at half maximum of about 150 meV (30 nm). The choice of In as the antisurfactant also avoids the incorporation of foreign atoms in the active layers. © 2002 American Institute of Physics.
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81.07.Ta Quantum dots
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.55.Cr III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
87.64.Ee Electron microscopy

Raman scattering and x-ray absorption studies of Ge–Si nanocrystallization

A. Kolobov, H. Oyanagi, N. Usami, S. Tokumitsu, T. Hattori, S. Yamasaki, K. Tanaka, S. Ohtake, and Y. Shiraki

Appl. Phys. Lett. 80, 488 (2002); http://dx.doi.org/10.1063/1.1435076 (3 pages) | Cited 19 times

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We have studied the local structure of GeSi nanocrystals embedded in SiO2 prepared by co-sputtering of Ge, Si, and SiO2 targets onto a Si(100) substrate. From Raman scattering, we conclude that the formation of the isotropic crystalline Ge phase starts at about 800 °C followed by the formation of a GeSi phase at higher temperatures. The formed nanocrystals, whose size depends on the annealing temperature, are randomly oriented. The local structure of the nanocrystals has been studied by x-ray absorption fine structure spectroscopy. They are found to consist of a relaxed Ge core with a typical diameter of ∼4 nm and the Ge–Ge bond length of 2.45 Å and of a GeSi outer shell, the Ge–Si bond length being 2.39 Å. The average composition of the grown nanocrystals is estimated to be Ge0.75Si0.25. © 2002 American Institute of Physics.
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78.30.Hv Other nonmetallic inorganics
78.66.Li Other semiconductors
78.70.Dm X-ray absorption spectra
68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials
61.72.Cc Kinetics of defect formation and annealing
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