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2 Apr 2001

Volume 78, Issue 14, pp. 1961-2084

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Monodispersed, nonagglomerated silicon nanocrystallites

Nobuyasu Suzuki, Toshiharu Makino, Yuka Yamada, Takehito Yoshida, and Takafumi Seto

Appl. Phys. Lett. 78, 2043 (2001); http://dx.doi.org/10.1063/1.1360236 (3 pages) | Cited 21 times

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We demonstrate the synthesis of monodispersed, nonagglomerated silicon (Si) nanocrystallites, using an integrated process system composed of a unit for the formation of nanocrystallites by pulsed-laser ablation in an inert background gas, a unit for classification using a differential mobility analyzer (DMA), and a unit for deposition onto a substrate using a nozzle jet. The DMA has been designed to operate under pressures less than 5.0 Torr. We have synthesized nonagglomerated Si nanocrystallites of 3.8 nm mean diameter and 1.2 geometrical standard deviation on carbon thin films using this integrated process system. © 2001 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
81.16.Mk Laser-assisted deposition
81.05.Cy Elemental semiconductors
61.46.-w Structure of nanoscale materials

Three-dimensional simulation of nanocrystal Flash memories

G. Iannaccone and P. Coli

Appl. Phys. Lett. 78, 2046 (2001); http://dx.doi.org/10.1063/1.1361097 (3 pages) | Cited 28 times

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We have developed a code for the detailed simulation of nanocrystal Flash memories, which consist of metal–oxide–semiconductor field-effect transistors (MOSFETs) with an array of semiconductor nanocrystals embedded in the gate dielectric. Information is encoded in the MOSFET threshold voltage, which depends on the amount of charge stored in the nanocrystal layer. Nanocrystals are charged through direct tunneling of electrons from the channel. Such memories are promising in terms of shorter write–erase times, larger cyclability, and lower power consumption with respect to conventional nonvolatile memories. We show results obtained from the self-consistent solution of the Poisson–Schrödinger equation on a three-dimensional grid, focusing on the charging process and on the effect of charge stored in the nanocrystals on the threshold voltage. © 2001 American Institute of Physics.
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85.30.Tv Field effect devices
85.35.-p Nanoelectronic devices
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
81.16.-c Methods of micro- and nanofabrication and processing
84.30.Sk Pulse and digital circuits
73.63.-b Electronic transport in nanoscale materials and structures
85.30.De Semiconductor-device characterization, design, and modeling

Overlayer-induced anisotropic alignment of Nd2Fe14B nanograins

T. Shima, A. Kamegawa, K. Hono, and H. Fujimori

Appl. Phys. Lett. 78, 2049 (2001); http://dx.doi.org/10.1063/1.1360234 (3 pages) | Cited 11 times

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Highly anisotropic Nd2Fe14B thin film has been produced by triggering crystallization of sputter-deposited amorphous Nd–Fe–B layer by deposition of crystalline Cr overlayer. A downward growth of strongly textured Nd2Fe14B columnar grains was observed, starting from the interface between the Nd–Fe–B amorphous layer and the Cr overlayer. Cross-sectional transmission electron microscope observation results suggest that the possible mechanism of this peculiar crystallization is the heterogeneous nucleation at the surface of Nd–Fe–B amorphous layer, triggered by the crystalline Cr overlayer. © 2001 American Institute of Physics.
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75.50.Vv High coercivity materials
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
75.50.Bb Fe and its alloys

Template-based carbon nanotubes and their application to a field emitter

Soo-Hwan Jeong, Hee-Young Hwang, Kun-Hong Lee, and Yongsoo Jeong

Appl. Phys. Lett. 78, 2052 (2001); http://dx.doi.org/10.1063/1.1359483 (3 pages) | Cited 86 times

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Anodic aluminum oxide (AAO) templates were fabricated by anodizing Al films. After the Co catalyst had been electrochemically deposited into the bottom of the AAO template, carbon nanotubes (CNTs) were grown by the catalytic pyrolysis of C2H2 at 650 °C. Overgrowth of CNTs on the AAO templates was observed. The diameter of the CNTs strongly depends on the size of the pores in the AAO template. The electron field emission measurements on the samples showed a turn-on field of 1.9–2.1 V/μm and a field enhancement factor of 3360–5200. Our observation concerning the low turn-on field and high field enhancement factors is explained in terms of a low field screening effect. © 2001 American Institute of Physics.
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81.07.De Nanotubes
81.16.Be Chemical synthesis methods
79.70.+q Field emission, ionization, evaporation, and desorption
85.45.Db Field emitters and arrays, cold electron emitters

Which nanowire couples better electrically to a metal contact: Armchair or zigzag nanotube?

M. P. Anantram

Appl. Phys. Lett. 78, 2055 (2001); http://dx.doi.org/10.1063/1.1360228 (3 pages) | Cited 18 times

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The fundamental question of how chirality affects the electronic coupling of a nanotube to metal contacts is important for the application of nanotubes as nanowires. We show that metallic-zigzag nanotubes are superior to armchair nanotubes as nanowires, by modeling the metal–nanotube interface. More specifically, we show that as a function of coupling strength, the total electron transmission of armchair nanotubes increases and tends to be pinned close to unity for a metal with Fermi wave vector close to that of gold. In contrast, the total transmission of zigzag nanotubes increases to the maximum possible value of two. The origin of these effects lies in the details of the wave function, which is explained. © 2001 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
61.46.-w Structure of nanoscale materials
73.63.Fg Nanotubes
85.35.Kt Nanotube devices

Two field-emission states of single-walled carbon nanotubes

R. Collazo, R. Schlesser, and Z. Sitar

Appl. Phys. Lett. 78, 2058 (2001); http://dx.doi.org/10.1063/1.1361089 (3 pages) | Cited 21 times

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Two field-emission states of single-walled carbon nanotubes have been identified according to their respective emission current levels. The state yielding increased emission current has been attributed to the presence of adsorbates on the nanotubes. It was realized that, by application of high electric fields inducing large emission currents, a transition between the two states could be induced. For the high current state, field-emitted electrons originated from states located 1 eV below the Fermi level, as was determined by field-emission energy distribution measurements. This suggested that adsorbates introduced a resonant state on the surface that enhanced the tunneling probability of the electrons. These states are removed when the nanotubes are cleaned by application of a large electric field, thus, decreasing the field-emitted current. © 2001 American Institute of Physics.
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71.20.Tx Fullerenes and related materials; intercalation compounds
79.70.+q Field emission, ionization, evaporation, and desorption
73.20.At Surface states, band structure, electron density of states

Mechanism of electron-beam writing in passivated gold nanoclusters

T. R. Bedson, R. E. Palmer, and J. P. Wilcoxon

Appl. Phys. Lett. 78, 2061 (2001); http://dx.doi.org/10.1063/1.1357210 (3 pages) | Cited 4 times

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We have investigated the mechanism of direct electron-beam writing in thin films of passivated gold nanoclusters. The exposure of films of approximately monolayer thickness (6 nm) was investigated as a function of electron dose on various substrates. Films were obtained on various substrates: graphite, silicon, thermally grown silicon dioxide and sputtered silicon dioxide. The experimental results are compared with Monte Carlo simulations of the electron scattering. We conclude that, in the case of such monolayer films, exposure of the clusters is dominated by electrons scattered in the substrate, so that the properties of the resist depend strongly on the nanocluster/substrate combination. © 2001 American Institute of Physics.
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81.16.Rf Micro- and nanoscale pattern formation
81.05.Bx Metals, semimetals, and alloys
81.07.Bc Nanocrystalline materials
81.65.Rv Passivation
02.70.Uu Applications of Monte Carlo methods
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