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1 Mar 2002

Volume 91, Issue 5, pp. 2563-3485

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Nanowires of four epitaxial hexagonal silicides grown on Si(001)

Yong Chen, Douglas A. A. Ohlberg, and R. Stanley Williams

J. Appl. Phys. 91, 3213 (2002); http://dx.doi.org/10.1063/1.1428807 (6 pages) | Cited 90 times

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Epitaxial self-assembled silicide nanowires can be grown on Si (001) if the magnitude of the lattice mismatch between epilayer and substrate is large along one crystal axis and small along the perpendicular axis. This phenomenon is illustrated with four examples: ScSi2, ErSi2, DySi2, and GdSi2, which have lattice mismatches of −4.6%, 6.3%, 7.6%, and 8.9%, respectively, along one of the Si 〈110〉 directions and mismatches of 0.8%, −1.6%, −0.1%, and 0.8%, respectively, along the perpendicular Si〈110〉 direction. The resulting self-assembled nanowires have widths and heights in the range of 3–11 and 0.2–3 nm, depending on the lattice mismatches. The average lengths of the nanowires are in the range 150–450 nm, and are determined primarily by kinetic issues. The epitaxial growth of silicide nanowires should prove interesting to those studying quasi-one- dimensional systems. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.16.Dn Self-assembly

Determination of the eigenfunctions of arbitrary nanostructures using time domain simulation

Dennis M. Sullivan and D. S. Citrin

J. Appl. Phys. 91, 3219 (2002); http://dx.doi.org/10.1063/1.1445277 (8 pages) | Cited 14 times

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With the present interest in nanostructures, such as quantum dots, there is a need to have a flexible method with which to be able to determine eigenvalues and eigenstates for those structures that do not lend themselves to existing analytical methods. In this article we present a method that accomplishes this by using a simulation of the Schrödinger equation based on the finite-difference time-domain method. This method is capable of simulating any structure within the limits of discretization. By initializing a simulation with a test function, the eigenfrequencies are determined through a Fourier transform of the resulting time-domain data collected at a sample point. Another simulation implements a discrete Fourier transform at the eigenfrequencies at every cell in the problem space, from which the eigenfunctions can be constructed. © 2002 American Institute of Physics.
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73.21.La Quantum dots
02.70.Bf Finite-difference methods
02.30.Nw Fourier analysis
02.30.Uu Integral transforms

Valence band structures of the InAs/GaAs quantum ring

Shu-Shen Li and Jian-Bai Xia

J. Appl. Phys. 91, 3227 (2002); http://dx.doi.org/10.1063/1.1446240 (5 pages) | Cited 21 times

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In the framework of effective-mass envelope function theory, the valence energy subbands and optical transitions of the InAs/GaAs quantum ring are calculated by using a four-band valence band model. Our model can be used to calculate the hole states of quantum wells, quantum wires, and quantum dots. The effect of finite offset and valence band mixing are taken into account. The energy levels of the hole are calculated in the different shapes of rings. Our calculations show that the effect of the difference between effective masses of holes in different materials on the valence subband structures is significant. Our theoretical results are consistent with the conclusion of the recent experimental measurements and should be useful for researching and making low-dimensional semiconductor optoelectronic devices. © 2002 American Institute of Physics.
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73.21.Fg Quantum wells
73.63.Hs Quantum wells
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

One-phonon Raman scattering studies of chains of crystalline-Si nanospheres

H. Kohno, T. Iwasaki, Y. Mita, and S. Takeda

J. Appl. Phys. 91, 3232 (2002); http://dx.doi.org/10.1063/1.1446222 (4 pages) | Cited 13 times

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Chains of crystalline-Si nanospheres were studied by means of Raman scattering spectroscopy. We found that the one-phonon Raman scattering peak from the chains was asymmetric and broader than that from bulk Si. This phenomenon can be attributed to a phonon confinement in the silicon nanospheres. The phonon confinement became more obvious by decreasing the size of the silicon nanospheres in the chains. We also found that the Si nanospheres in the chains were under compressive stress by the covering oxide layers through the analysis of the Raman shift. © 2002 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.46.-w Structure of nanoscale materials
78.30.Am Elemental semiconductors and insulators

Controlling the formation of luminescent Si nanocrystals in plasma-enhanced chemical vapor deposited silicon-rich silicon oxide through ion irradiation

T. G. Kim, C. N. Whang, Yohan Sun, Se-Young Seo, Jung H. Shin, and J. H. Song

J. Appl. Phys. 91, 3236 (2002); http://dx.doi.org/10.1063/1.1432114 (7 pages) | Cited 5 times

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The effect of ion irradiation on the formation of luminescent Si nanocrystals from silicon-rich silicon oxide (SRSO) films deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition (PECVD) whose Si content ranged from 33 to 50 at. % is investigated. As-deposited SRSO films contained a high density of irregular-shaped Si nanocrystals. Irradiating these films with 380 keV Si at room temperature to a dose of 5.7×1015 cm−2 prior to anneal at 1000 °C is found to increase the luminescence intensity due to Si nanocrystals over the films. Based on the x-ray photoemission spectra and the dependence of the luminescence intensity on the irradiating ion dose, anneal time, and the silicon content of the film, we propose the destruction of pre-existing Si clusters by ion irradiation to be an important factor responsible for the observed enhancement of luminescence, and suggest that preanneal irradiation may be a viable method to control the formation of luminescent Si nanocrystals in PECVD-deposited silicon-rich silicon oxide. © 2002 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Ap Elemental semiconductors
61.80.Jh Ion radiation effects
52.77.Dq Plasma-based ion implantation and deposition
61.72.Cc Kinetics of defect formation and annealing
61.46.-w Structure of nanoscale materials
61.82.Rx Nanocrystalline materials
78.66.Nk Insulators
68.55.-a Thin film structure and morphology
81.07.Bc Nanocrystalline materials

Highly ordered monocrystalline silver nanowire arrays

G. Sauer, G. Brehm, S. Schneider, K. Nielsch, R. B. Wehrspohn, J. Choi, H. Hofmeister, and U. Gösele

J. Appl. Phys. 91, 3243 (2002); http://dx.doi.org/10.1063/1.1435830 (5 pages) | Cited 146 times

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Highly ordered silver nanowire arrays have been obtained by pulsed electrodeposition in self-ordered porous alumina templates. Homogeneous filling of all the pores of the alumina template is achieved. The interwire distance is about 110 nm corresponding to a density of silver nanowires of 61×109 in.−2 and the diameter can be varied between 30 and 70 nm. The silver wires are monocrystalline with some twin lamella defects and grow perpendicular to the 〈110〉 direction. The previously encountered difficulty to obtain 100% filling of the alumina pores is discussed in the framework of electrostatic instabilities taking into account the different potential contributions during electrodeposition. To obtain homogeneously filled pore membranes, a highly conductive metal containing electrolyte, a homogeneous aluminum oxide barrier layer, and pulsed electrodeposition are a prerequisite. © 2002 American Institute of Physics.
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81.07.Vb Quantum wires
81.15.Pq Electrodeposition, electroplating
68.65.La Quantum wires (patterned in quantum wells)
81.07.Bc Nanocrystalline materials
73.63.Nm Quantum wires
82.45.Qr Electrodeposition and electrodissolution

Correlation between photoluminescence properties and morphology of laser-ablated Si/SiOx nanostructured films

A. V. Kabashin, J.-P. Sylvestre, S. Patskovsky, and M. Meunier

J. Appl. Phys. 91, 3248 (2002); http://dx.doi.org/10.1063/1.1446217 (7 pages) | Cited 37 times

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Pulsed laser ablation in an inert gas has been used to fabricate films containing silicon nanocrystals. We show that film microstructure is one of the main factors, determining long-term photoluminescence (PL) properties. Films with different porosity were found to exhibit PL signals with quite different peak energies, integral intensities and time-dependent evolutions. The distinction of these PL properties is attributed to the different efficiency of surface chemistry interactions between Si nanocrystallites and the ambient atmosphere for films having different porosities. Oxygen-related defects and other mechanisms are discussed to explain the PL properties of the films. © 2002 American Institute of Physics.
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78.66.-w Optical properties of specific thin films
78.55.-m Photoluminescence, properties and materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials

Thermal stability of stacked self-assembled InP quantum dots in GaInP

N. Y. Jin-Phillipp, K. Du, F. Phillipp, M. Zundel, and K. Eberl

J. Appl. Phys. 91, 3255 (2002); http://dx.doi.org/10.1063/1.1446656 (6 pages) | Cited 4 times

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Thermal stability of stacked self-assembled InP quantum dots (QDs) embedded in Ga0.51In0.49P (GaInP) under ex situ rapid thermal annealing (RTA) is studied by photoluminescence spectroscopy and quantitative high-resolution electron microscopy. It is found that InP QDs intermix with surrounding GaInP, and that this is enhanced with increasing temperature and duration of RTA. The preferential direction of the intermixing and reshaping of the QDs changes at different stages of RTA. This anisotropy is attributed to strain-assisted interdiffusion, and is expected in stacked QDs of other material systems. © 2002 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
81.07.Ta Quantum dots
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
68.60.Dv Thermal stability; thermal effects
81.16.Dn Self-assembly

Picosecond ultrasonics study of the vibrational modes of a nanostructure

G. Andrew Antonelli, Humphrey J. Maris, Sandra G. Malhotra, and James M. E. Harper

J. Appl. Phys. 91, 3261 (2002); http://dx.doi.org/10.1063/1.1435831 (7 pages) | Cited 40 times

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We report experiments in which a subpicosecond pump light pulse is used to excite vibrations in a nanostructure consisting of a periodic array of copper wires embedded in a glass matrix on a silicon substrate. The motion of the wires after excitation is detected using a time-delayed probe light pulse. From the measured data, it is possible to determine the frequencies νn and damping rates Γn of a number of the normal modes of the structure. These modes have frequencies lying in the range 1–30 GHz. By comparison of the measured νn and Γn with the frequencies and damping rates calculated from a computer simulation of the vibrations of the nanostructure, we have been able to deduce the vibration patterns of six of the normal modes. © 2002 American Institute of Physics.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
68.35.Ja Surface and interface dynamics and vibrations
62.65.+k Acoustical properties of solids

Pulsed-laser assisted nanopatterning of metallic layers combined with atomic force microscopy

S. M. Huang, M. H. Hong, Y. F. Lu, B. S. Lukỳanchuk, W. D. Song, and T. C. Chong

J. Appl. Phys. 91, 3268 (2002); http://dx.doi.org/10.1063/1.1448882 (7 pages) | Cited 38 times

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Pulsed-laser assisted nanopatterning of metallic layers on silicon substrates under an atomic force microscope (AFM) tip has been investigated. A 532 nm Nd:YAG pulsed laser with a pulse duration of 7 ns was used. Boron doped silicon tips were used in contact mode. This technique enables processing of structures with a lateral resolution down to 10 nm on the copper layers. Nanopatterns such as pit array and multilines with lateral dimensions between 10 and 60 nm and depths between 1.5 and 7.0 nm have been created. The experimental results and mechanism of the nanostructure formation are discussed. The created features were characterized by AFM, scanning electron microscope and Auger electron spectroscopy. The apparent depth of the created pit has been studied as a function of laser intensity or laser pulse numbers. Dependence of nanoprocessing on the geometry parameters of the tip and on the optical and thermal properties of the processed sample has also been investigated. Thermal expansion of the tip, the field enhancement factor underneath the tip, and the sample surface heating were estimated. It is proposed that field-enhancement mechanism is the dominant reason for this nanoprocessing. © 2002 American Institute of Physics.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Ta Atom manipulation
07.79.Lh Atomic force microscopes
42.62.-b Laser applications

Processing dependent thermal conductivity of nanoporous silica xerogel films

Anurag Jain, Svetlana Rogojevic, Shom Ponoth, William N. Gill, Joel L. Plawsky, Eva Simonyi, Shyng-Tsong Chen, and P. S. Ho

J. Appl. Phys. 91, 3275 (2002); http://dx.doi.org/10.1063/1.1448407 (7 pages) | Cited 18 times

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Sintered xerogel films (porous SiO2) show a much higher thermal conductivity than other low dielectric constant (low-K) materials available for the same value of K. The thermal conductivity of xerogels which we have processed using different methods is compared with that of other low-K materials such as silica hybrid (silsesquioxanes) and polymeric low-K materials. The methods used were: (1) single solvent (ethanol) method, (2) binary solvent (mixture of ethanol and ethylene glycol) method, (3) sintering. For the xerogel films, we show that process history is as important as the chemistry of the solid matrix or the porosity in determining the thermal conductivity. The thermal conductivity, measured by the 3-ω method or the photothermal deflection method, is affected by phonon scattering, which in turn is effected by the size and distribution of pores and particles and the presence of imperfections such as interfaces, substituted chemical species, impurities, microcracks, and microporosity. The thermal conductivity extrapolated to zero porosity for porous sintered xerogel films approaches that of thermally grown SiO2 indicating the least phonon scattering of all processing methods. For these films, the elastic modulus is proportional to thermal conductivity squared, in agreement with theories developed for materials with few defects and a connected matrix. © 2002 American Institute of Physics.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.60.Dv Thermal stability; thermal effects
61.46.-w Structure of nanoscale materials
61.43.Gt Powders, porous materials
82.70.Gg Gels and sols
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
62.20.D- Elasticity

Nanoscale limited area growth of InAs islands on GaAs(001) by molecular beam epitaxy

S. C. Lee, A. Stintz, and S. R. J. Brueck

J. Appl. Phys. 91, 3282 (2002); http://dx.doi.org/10.1063/1.1436303 (7 pages) | Cited 20 times

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Growth of InAs islands on a GaAs(001) substrate patterned with ∼50–200-nm diameter holes in an SiO2 mask overlayer providing selective GaAs nucleation areas is reported. The nanoscale pattern was generated in the SiO2 film by large-area interferometric lithography and dry etching. Two-dimensional, 285-nm period, arrays of InAs islands having heights of 10–15 nm with three different bottom diameters of 50–100, ∼150, and ∼200 nm were selectively grown on SiO2 patterned substrates by molecular beam epitaxy. Growth conditions were chosen to provide a very-low sticking coefficient of In atoms on the SiO2 surface suppressing volume contribution from migration of In atoms incident on the SiO2 mask region to nearby open GaAs surface areas. Formation of spherical-section InAs dots with diameters of about 50 nm relying on nanoscale-limited area growth is demonstrated. As the diameter of the hole increases beyond 150 nm, InAs islands deviate from a spherical section and self-assembled quantum dots confined within the open GaAs surface appear. A relation between dot formation and the nanoscale growth area is proposed, with a transition from single- to multiple-dot formation occurring at hole diameters of ∼100–150 nm. © 2002 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.16.Dn Self-assembly
68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
81.05.Ea III-V semiconductors

Quantum phase interference in nanomagnets with tetragonal symmetry

Gwang-Hee Kim

J. Appl. Phys. 91, 3289 (2002); http://dx.doi.org/10.1063/1.1450028 (5 pages) | Cited 3 times

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Employing a spin-coherent-state path integral method, we study the spin-parity dependence of the tunnel splitting in the uniaxial system with tetragonal symmetry. The tunnel splitting is found to vanish for magnetic particles with half integer or odd number spin. Applying an external magnetic field along the hard axis, we find that topological effect results in oscillation of the tunnel splitting, and present the relation between the quenching period and the ratio of two anisotropy constants of the nanomaget with any total spin including molecular magnets. © 2002 American Institute of Physics.
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73.23.-b Electronic transport in mesoscopic systems
72.25.-b Spin polarized transport
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Xx Molecular magnets
85.75.Mm Spin polarized resonant tunnel junctions
75.45.+j Macroscopic quantum phenomena in magnetic systems

Mechanisms of visible photoluminescence from nanoscale silicon cones

A. Wellner, R. E. Palmer, J. G. Zheng, C. J. Kiely, and K. W. Kolasinski

J. Appl. Phys. 91, 3294 (2002); http://dx.doi.org/10.1063/1.1448394 (5 pages) | Cited 6 times

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We explore the origin of visible photoluminescence in nanoscale silicon cones fabricated by reactive ion etching in silicon-on-insulator substrates utilizing rough silver films as masks. Photoluminescence (PL) visible to the naked eye was observed after oxidation and annealing. Samples oxidized at 900 °C exhibit intense yellow/green photoluminescence centered at about 530 nm. Samples oxidized at 1000 °C luminesce in the red-to-infrared region with peak positions between 650 and 730 nm. Transmission electron microscopy characterization is employed to show that PL at 530 nm can be understood in terms of defect states, while the PL at 650–730 nm can be explained by a combination of defect state and quantum confinement effects. © 2002 American Institute of Physics.
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78.55.Ap Elemental semiconductors
81.65.Mq Oxidation
81.65.Cf Surface cleaning, etching, patterning
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.55.Cn Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing

Photonic-band-gap properties of two-dimensional lattices of Si nanopillars

Vladimir V. Poborchii, Tetsuya Tada, and Toshihiko Kanayama

J. Appl. Phys. 91, 3299 (2002); http://dx.doi.org/10.1063/1.1446659 (7 pages) | Cited 20 times

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We studied photonic-band-gap properties of two-dimensional lattices of Si nanopillars by theoretical calculation and measurement of reflection and transmission spectra. We focused on advantages of these photonic crystals compared to other Si photonic crystals, which usually operate in the range of transparency of bulk Si (wavelengths longer than ∼1.1 μm). We showed that the available spectral range for the photonic crystals of Si nanopillars can be extended to the submicron wavelengths, light absorption by Si nanopillars being insignificant. Another important advantage of Si nanopillar lattices is the ability to incorporate luminescent materials into the huge free space of this photonic crystal. We demonstrate the inhibition of spontaneous emission of dye incorporated into the nanopillar lattice. © 2002 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.70.Qs Photonic bandgap materials
78.40.Fy Semiconductors
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