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22 Oct 2001

Volume 79, Issue 17, pp. 2681-2850

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Nonlinear ground-state absorption observed in a single quantum dot

Evelin Beham, Artur Zrenner, Frank Findeis, Max Bichler, and Gerhard Abstreiter

Appl. Phys. Lett. 79, 2808 (2001); http://dx.doi.org/10.1063/1.1411987 (3 pages) | Cited 23 times

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We report level bleaching in the ground state of a single In0.5Ga0.5As quantum dot. This behavior arises from the nonlinear absorption of a single quantum state. The level bleaching is observed in terms of a saturation of the photocurrent with increasing excitation power under the condition of resonant excitation in the quantum dot ground state. Furthermore, the photocurrent saturation is put down to a fundamental rate equation model. The steady-state solutions are in good agreement with the experimentally observed power dependence of the photocurrent. © 2001 American Institute of Physics.
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73.21.La Quantum dots
78.67.Hc Quantum dots
73.50.Pz Photoconduction and photovoltaic effects
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

High-current field emission from a vertically aligned carbon nanotube field emitter array

J. T. L. Thong, C. H. Oon, W. K. Eng, W. D. Zhang, and L. M. Gan

Appl. Phys. Lett. 79, 2811 (2001); http://dx.doi.org/10.1063/1.1412590 (3 pages) | Cited 37 times

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Arrays of vertically aligned carbon nanotubes (CNTs) were grown on a patterned sputtered cobalt film by chemical vapor deposition from ethylenediamine at 900 °C. Each square array comprises a moderate density of nanotubes with an average height of 90 μm covering a total area of 3.6×10−3 cm2. Field emission measurements were carried out on individual arrays at pressures below 10−8 mbar. The spacing between the anode and the top of the CNT array is 935 μm and a total current of 2 mA could be obtained at 2.5 kV. A Fowler–Nordheim plot of the I–V data shows an unusually high field enhancement factor at lower fields. At an average field strength of 1.925 V/μm, the corresponding emission current density is 130 mA/cm2. This emission current was found to be very stable, with short-term fluctuations (5 Hz measurement bandwidth) of no more than ±1.5%, while the current drifted less than 1.5% over a test period of 20 h. © 2001 American Institute of Physics.
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85.45.Db Field emitters and arrays, cold electron emitters
81.07.De Nanotubes
85.35.Kt Nanotube devices
79.70.+q Field emission, ionization, evaporation, and desorption
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Growth and magneto-optical properties of sub 10 nm (Cd, Mn)Se quantum dots

P. R. Kratzert, J. Puls, M. Rabe, and F. Henneberger

Appl. Phys. Lett. 79, 2814 (2001); http://dx.doi.org/10.1063/1.1413735 (3 pages) | Cited 25 times

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We report on the formation of self-assembled semimagnetic (Cd, Mn)Se quantum dots via thermally activated reorganization of an initially two-dimensional film. Incorporation of Mn causes a marked decrease of the dot density, while the size is only slightly affected. Magneto-optical data are consistent with a homogeneous distribution of the magnetic ions. We observe g factors as large as 200, enabling control of individual carrier spins on a sub 10 nm length scale. © 2001 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
81.07.Ta Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.20.Ls Magneto-optical effects

Self-assembled epitaxial and polycrystalline magnetic nickel nanocrystallites

D. Kumar, H. Zhou, T. K. Nath, Alex V. Kvit, and J. Narayan

Appl. Phys. Lett. 79, 2817 (2001); http://dx.doi.org/10.1063/1.1412428 (3 pages) | Cited 17 times

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Nanocrystalline nickel particles were embedded in amorphous alumina and crystalline TiN matrices using a pulsed-laser deposition process to investigate the effect of texturing on magnetic properties of nickel nanocrystallites. The crystalline quality of both the matrix and magnetic particles were investigated by cross-sectional high-resolution transmission electron microscopy. The embedded Ni nanocrystals were found to be epitaxial in case of TiN matrix and polycrystalline in Al2O3 amorphous matrix. The Ni nanocrystals on TiN/Si grow epitaxially because the TiN acting as a template grows epitaxially on Si substrate via domain epitaxy. On the other hand, Ni nanocrystals in Al2O3 matrix are polycrystalline because of the amorphous nature of the alumina matrix. Magnetization versus temperature measurements have shown that the blocking temperature, above which the samples lose magnetization-field (M–H) hysteretic behavior, of Ni–TiN sample (∼190 K) is significantly higher than that of Ni–Al2O3 sample (∼30 K) with a similar size distribution of embedded magnetic particles. A comparison of the values of coercivity (Hc) of the two samples, measured from M–H data, indicates that epitaxial Ni nanocrystals also exhibit significantly higher coercivity than polycrystalline Ni particles. The high values of TB and Hc of Ni–TiN samples with respect to TB of Ni–Al2O3 samples are believed to be associated with preferred alignment of nanocrystallites. © 2001 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials
81.16.Dn Self-assembly
68.37.Lp Transmission electron microscopy (TEM)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Nanolithography of silicon: An approach for investigating tip-surface interactions during writing

R. D. Ramsier, R. M. Ralich, and S. F. Lyuksyutov

Appl. Phys. Lett. 79, 2820 (2001); http://dx.doi.org/10.1063/1.1413736 (3 pages) | Cited 4 times

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We report an approach for monitoring tip-surface interactions. The approach is based on power spectrum analysis of atomic force microscope (AFM) tip oscillations during scanning probe nanolithography on Si surfaces. A single mode harmonic oscillator model allows us to determine the main characteristics of the AFM tip-surface interaction: the amplitude of oscillation, the resonant frequency, and the damping factor, during the writing process. We measure these quantities in scanning probe anodization versus the bias voltage. By fixing the length of lithographically patterned lines, and the energy deposited into each line, we search for trends which may reveal the major factors controlling the quality of AFM-written nanostructures. Our data are consistent with the concepts that a water meniscus and electrostatic tip-surface interactions dominate contact AFM lithography. © 2001 American Institute of Physics.
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81.05.Cy Elemental semiconductors
81.16.Nd Micro- and nanolithography
07.79.Lh Atomic force microscopes
81.16.Ta Atom manipulation

Quantum waveguide array generator for performing Fourier transforms: Alternate route to quantum computing

R. Akis and D. K. Ferry

Appl. Phys. Lett. 79, 2823 (2001); http://dx.doi.org/10.1063/1.1413500 (3 pages) | Cited 4 times

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Recently, quantum computing has gained attention as a possible means of greatly increasing the speed of certain calculations when compared with traditional, binary computing. A key part of many quantum computing algorithms is the performance of a Fourier transform. In this letter, we propose a quantum waveguide array device that can perform such operations quickly with a parallel approach that uses the analog properties of waves and rather than the qubit concept. © 2001 American Institute of Physics.
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03.67.Lx Quantum computation architectures and implementations
02.30.Nw Fourier analysis
02.30.Uu Integral transforms

Spontaneous formation of ordered indium nanowire array on Si(001)

Jian-Long Li, Xue-Jin Liang, Jin-Feng Jia, Xi Liu, Jun-Zhong Wang, En-Ge Wang, and Qi-Kun Xue

Appl. Phys. Lett. 79, 2826 (2001); http://dx.doi.org/10.1063/1.1413722 (3 pages) | Cited 24 times

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Growth of In on the Si(001)-2×n nanostructured surface is investigated by an in situ scanning tunneling microscope (STM). The deposited In atoms predominantly occupy the normal 2×1 dimer-row structure, and develop into a uniform array of In nanowires at a coverage of ∼0.2 ML. High-resolution STM images show that the In atoms form a stable local 2×2 reconstruction that removes surface Si dangling bonds states and saturates all In valency. Since the dimensions of the Si(001)-2×n vacancy line structure depend on impurity concentrations, this study demonstrates that the 2×n surface can be used for spontaneous fabrication of various metal nanowire arrays. © 2001 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
68.43.Hn Structure of assemblies of adsorbates (two- and three-dimensional clustering)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Rh Phase transitions and critical phenomena

Asymmetry in negative differential resistance driven by electron–electron interactions in two-site molecular devices

J. E. Han and Vincent H. Crespi

Appl. Phys. Lett. 79, 2829 (2001); http://dx.doi.org/10.1063/1.1413499 (3 pages) | Cited 7 times

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We demonstrate that Coulomb interactions within the Hartree–Fock approximation can induce a strong asymmetry in the negative differential resistance of a two-site resonant molecular device. This sharp cutoff at high voltage is generic and independent of the detailed single-particle electronic structure of the system. The intersite coupling between distinct molecular subunits controls a transition from staircase to resonant current–voltage characteristics. These studies clarify the relationship between weak screening and strong nonlinearity. © 2001 American Institute of Physics.
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81.07.Nb Molecular nanostructures
85.65.+h Molecular electronic devices
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
73.20.At Surface states, band structure, electron density of states
73.23.Hk Coulomb blockade; single-electron tunneling
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